Piston rod assembly for a paint pump

ABSTRACT

A wear sleeve is removably mounted on a piston rod. The piston rod includes a piston cap, a piston rod body, and a piston head, with at least one of the piston cap and the piston head being removable from the piston rod body. The wear sleeve is disposed over the piston rod body and prevents the piston rod from contacting dynamic seals disposed within a pump. The wear sleeve is mechanically secured in a cylindrical recess on the piston rod between a cap shoulder of the piston cap and a head shoulder of the piston head.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.15/901,404 filed Feb. 21, 2018 for “REMOVABLE PISTON ROD SLEEVE FORFLUID PUMP” by J. D. Horning and S. J. Wrobel, which in turn claims thebenefit of U.S. Provisional Application No. 62/461,575 filed Feb. 21,2017, and entitled “REMOVEABLE PISTON ROD SLEEVE FOR FLUID PUMP,” thedisclosures of which are hereby incorporated in their entirety.

BACKGROUND

This disclosure relates generally to piston rods. More particularly,this disclosure relates the removable wear sleeves for piston rods.

Fluid dispensing systems, such as fluid dispensing systems for paint andother solutions, typically utilize axial displacement pumps to pull afluid from a source and to drive the fluid downstream. The axialdisplacement pump includes a piston that is driven in a reciprocatorymanner along its longitudinal axis to pump the fluid. As the pistonreciprocates, fluid is drawn into the pump and driven downstream.Displacement pumps include dynamic seals to prevent fluid from leakingaround the piston. The piston can experience significant wear due to acombination of factors, such as the high pressures produced duringpumping; the cyclic relative movement of the interfacing parts, such asthe piston and the dynamic seal; and the abrasive nature of the fluidbeing pumped. Even where the piston is formed from a high-grade hardenedsteel, the abrasive nature of the pumped fluid and the high pressurescan cause excessive wear on the piston. If the piston becomes worn, thenthe entire piston requires replacement.

SUMMARY

According to one aspect of the disclosure, a piston rod for a pumpincludes a piston rod body elongate between a first end and a secondend, a piston cap connected to the first end, and a piston headconnected to the second end. The piston cap includes a cap shoulderextending radially relative to the first end. The piston head includes ahead shoulder extending radially relative to the second end. Acylindrical relief extends around the piston rod body between the capshoulder and the head shoulder, and the cylindrical relief is capable ofreceiving a wear sleeve. The piston rod body is removably connected toat least one of the piston cap and the piston head.

According to another aspect of the disclosure, a pump includes acylinder having an upstream end and a downstream end, a dynamic sealmounted in the cylinder, and a piston extending into the cylinder andthrough the first dynamic seal. The piston is configured to reciprocatewithin the cylinder and relative to the dynamic seal. The pistonincludes a piston rod body elongate between a first end and a secondend, a piston cap connected to the first end and including a capshoulder, a piston head connected to the second end and including a headshoulder, a cylindrical relief extending around the piston rod bodybetween the cap shoulder and the head shoulder, and a wear sleevemounted on the piston rod body within the cylindrical relief. The capshoulder extends radially relative to the first end. The head shoulderextends radially relative to the second end. The cylindrical reliefextends between the cap shoulder and the head shoulder. The piston rodbody is removably connected to at least one of the piston cap and thepiston head. An outer surface of the wear sleeve is the only portion ofthe piston contacting the dynamic seal during reciprocating pump strokesof the piston within the cylinder.

According to yet another aspect of the disclosure, a method of replacinga wear sleeve includes separating a first part of a piston rod from asecond part of the piston rod; sliding a first wear sleeve off of apiston rod body of the piston rod; sliding a second wear sleeve onto thepiston rod body; and clamping the second wear sleeve between an upstreamshoulder of the piston rod and a downstream shoulder of the piston rodby joining the first part of the piston rod to the second part secondpart of the piston rod.

According to yet another aspect of the disclosure, a removable sleevefor a piston rod having a piston cap, a piston head, and a piston rodbody extending between and removably connected to at least one of thepiston cap and the piston head includes a first end configured to abut acap shoulder of the piston cap; a second end configured to abut a headshoulder of the piston head; and a cylindrical sleeve body extendingbetween the first end and the second end. The cylindrical sleeve bodyreceives the piston rod body. The cylindrical sleeve body is formed froma ceramic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an isometric view of a fluid dispensing system.

FIG. 1B is an exploded view of a fluid dispensing system.

FIG. 2A is an isometric view of a displacement pump.

FIG. 2B is a cross-sectional view of the displacement pump of FIG. 2Ataken along line B-B shown in FIG. 2A.

FIG. 3A is an exploded view of a piston.

FIG. 3B is a cross-sectional view of a piston.

FIG. 4A is an exploded view of a piston.

FIG. 4B is a cross-sectional view of a piston.

FIG. 5A is a cross-sectional view of a displacement pump.

FIG. 5B is an exploded view of a piston.

FIG. 5C is a cross-sectional view of a piston.

FIG. 6A is an exploded view of a piston.

FIG. 6B is a cross-sectional view of a piston.

DETAILED DESCRIPTION

Pumps according to the present disclosure reciprocate a piston within acylinder to pump various fluids, examples of which include paint, water,oil, stains, finishes, aggregate, coatings, and solvents, amongst otheroptions. A piston pump can generate high fluid pumping pressures, suchas 3,000-5,000 pounds per square inch or even higher. High fluid pumpingpressure is useful for atomizing the fluid into a spray for applying thefluid to a surface. The generation of high fluid pumping pressure cancause accelerated wear in the components of the pump which reciprocaterelative to one another. Aspects of the present disclosure can reduce orminimize the effects of wear in a piston pump, as further discussedherein.

FIG. 1A is an isometric view of fluid dispensing system 10. FIG. 1B isan exploded view of fluid dispensing system 10. FIGS. 1A and 1B will bediscussed together. Fluid dispensing system 10 includes frame 12, motorsection 14, drive housing 16, displacement pump 18, reciprocating drive20 (FIG. 1B), control system 22, intake hose 24, supply hose 26,dispensing hose 28, housing cover 30, and handle 32. As shown in FIG.1B, motor section 14 includes motor housing 34 and drive gears 36, anddrive gear 36 includes eccentric drive pin 37. Drive housing 16 includesupper portion 38 and lower portion 40. Upper portion 38 includes gearaperture 42 and link aperture 44. Lower portion 40 includes mountingcavity 46 and guard 48. As shown in FIG. 1B, displacement pump 18includes piston 50 (which includes piston rod 52 and wear sleeve 54(shown in FIGS. 2B-6B)), cylinder 56, intake housing 58, and clamp 60.Cylinder 56 includes upstream end 62, downstream end 64, and outlet port66. Intake housing 58 includes inlet port 68. Reciprocating drive 20includes connecting rod 70 and drive link 72. Control system 22 includescontrol housing 74. Intake hose 24 includes intake fitting 76, andsupply hose 26 includes supply fitting 78.

Frame 12 supports motor section 14, and drive housing 16 is mounted tomotor section 14. Fasteners 80 a (FIG. 1B) extend through drive housing16 and into motor section 14 to secure drive housing 16 to motor section14. Handle 32 is attached to drive housing 16 by fastener 80 b (FIG.1B), which extends through drive housing 16 and into handle 32. Housingcover 30 is attached to and encloses upper portion 38 of drive housing16. Drive gears 36 are disposed within motor section 14 and extend intoupper portion 38 of drive housing 16 through gear aperture 42. Drivegears 36 are driven by a motor (not shown) disposed within motor housing34. Eccentric drive pin 37 extends into upper portion 38 and isconfigured to engage connecting rod 70. Any desired motor can beutilized to power drive gears 36. For example, fluid dispensing system10 can be electric, pneumatic, or hydraulic powered.

Upper portion 38 of drive housing 16 is integral with lower portion 40of drive housing 16. Gear aperture 42 extends through a rearward side ofupper portion 38, and link aperture 44 extends through drive housing 16between upper portion 38 and lower portion 40. Mounting cavity 46extends into lower portion 40 and is configured to receive displacementpump 18. Guard 48 is mounted on lower portion 40 and is configured tocover mounting cavity 46.

Reciprocating drive 20 is disposed within drive housing 16. Drive link72 is attached to connecting rod 70. Connecting rod 70 is disposedwithin upper portion 38 of drive housing, and drive link 72 extendsthrough link aperture 44 and into mounting cavity 46. Connecting rod 70is attached to and driven by drive gears 36 extending into upper portion38 through gear aperture 42. Connecting rod 70 and eccentric drive pin37 translate the rotational movement of drive gears 36 into linearmovement of drive link 72.

Displacement pump 18 is at least partially disposed within mountingcavity 46 and can be secured by clamp 60. Clamp 60 extends aboutcylinder 56, and clamp 60 secures displacement pump 18 to lower portion40 of drive housing 16. While displacement pump 18 is described as beingsecured to drive housing 16 by clamp 60 disposed on cylinder 56, it isunderstood that displacement pump 18 can be mounted in any suitablemanner. For example, displacement pump 18 can include external threadsconfigured to mate with threading on drive housing 16, or displacementpump 18 can be secured by a clamping mechanism integral with drivehousing 16.

Intake housing 58 is attached to upstream end 62 of cylinder 56 to forma body of displacement pump 18. Piston 50 is at least partially disposedwithin displacement pump 18. Piston rod 52 extends into cylinder 56through downstream end 64 of cylinder 56. An end of piston rod 52extending out of cylinder 56 is connected to drive link 72, and drivelink 72 is configured to drive piston rod 52 in a reciprocating manner.Piston rod 52 can be connected to drive link 72 in any suitable manner;for example, piston rod 52 can include a head mounted in a slot in drivelink 72, or piston rod 52 can be pinned to drive link 72.

Intake hose 24 extends between a fluid source and displacement pump 18.Intake fitting 76 is connected to inlet port 68 to provide the fluid tointake housing 58. Supply hose 26 extends between outlet port 66 ofcylinder 56 and control housing 74, to provide the fluid fromdisplacement pump 18 to control housing 74. Supply fitting 78 isconnected to outlet port 66 to attached supply hose 26 to displacementpump 18. Dispensing hose 28 is connected to control housing 74 andextends between control housing 74 and a dispenser (not shown), such asa spray gun. Control system 22 includes various components, such as apressure regulator and a priming valve, utilized to set a flow rate andflow pressure, among other operational criteria, of the fluid.Dispensing hose 28 provides the fluid downstream of fluid dispensingsystem 10.

During operation, the motor of motor section 14 drives drive gears 36 ina rotational manner, and connecting rod 70 follows drive gears 36 due tothe connection of eccentric drive pin 37 and connecting rod 70.Connecting rod 70 translates the rotational movement of drive gears 36into linear movement of drive link 72, such that drive link 72reciprocates through link aperture 44. Drive link 72 thereby drivespiston 50 in a reciprocating manner, due to the connection of piston rod52 and drive link 72. Driving piston 50 in a reciprocating manner causespiston 50 to draw the fluid into displacement pump 18 through intakehose 24 and intake housing 58, and to pump the fluid downstream throughcylinder 56 and supply hose 26.

The fluid is drawn from an external source (e.g., a bucket) throughintake hose 24 and enters displacement pump 18 through inlet port 68.The fluid is driven through displacement pump 18 by piston 50, and thefluid exits displacement pump 18 through outlet port 66 in cylinder 56.The fluid flows into supply hose 26 from outlet port 66 and flows tocontrol housing 74. The fluid exits control housing 74 throughdispensing hose 28 and flows downstream to the dispenser, where thefluid can be dispensed for any desired purpose, such as applying paintto a surface with a spray gun. Displacement pump 18 thus draws the fluidfrom a container through intake hose 24, drives the fluid downstream tocontrol system 22 through supply hose 26, and drives the fluid throughdispensing hose 28 and to a dispenser where the fluid is applied in anydesired manner.

FIG. 2A is an isometric view of displacement pump 18. FIG. 2B is across-sectional view of displacement pump 18 taken along line B-B inFIG. 2A. Displacement pump 18 includes piston 50, cylinder 56, intakehousing 58, first check valve 82, second check valve 84, first dynamicseal 86 a, and second dynamic seal 86 b. Piston 50 includes piston rod52 and wear sleeve 54. Piston rod 52 includes piston cap 88, piston rodbody 90, and piston head 92. Wear sleeve 54 includes sleeve body 94,first end 96, and second end 98. Piston cap 88 includes socket 100, capshoulder 102, and connecting portion 104. Piston rod body 90 includesupstream end 106, downstream end 108, seal groove 110, and shank 112.Piston head 92 includes central bore 114, flange 116, head shoulder 118,and relief 119. Cylinder 56 includes outlet port 66 (shown in FIG. 2A),first fluid chamber 120, second fluid chamber 122, and inner cylinderportion 124. Intake housing 58 includes inlet port 68. First check valve82 includes cage 126, first ball 128, and first seat 130. Second checkvalve 84 includes second ball 132, second seat 134, and retainer 136.Dynamic seal 86 a includes packing rings 138 a and seal glands 140 a,and dynamic seal 86 b includes packing rings 138 b and seal glands 140b. A generally downstream direction is indicated by downstream arrow,and a generally upstream direction is indicated by upstream arrow.

Intake housing 58 is mounted to cylinder 56. Outlet port 66 extendsthrough cylinder 56. Piston 50 is at least partially disposed withincylinder 56. Piston 50 extends along longitudinal axis L-L, withlongitudinal axis L-L oriented coaxially with the generally elongateprofile of displacement pump 18. Piston rod 52 extends into cylinder 56through cap 63 and packing nut 65. Piston rod 52 is elongate alonglongitudinal axis L-L. Piston rod 52 can be formed from any suitablydurable material for withstanding the high pressures associated withpumping. For example, piston rod 52 can be machined or cast from steel,brass, aluminum, or any other suitable metal. In some examples, pistonrod 52 can be formed from hardened 440C stainless steel. The componentsof piston rod 52, such as piston cap 88, piston rod body 90, and pistonhead 92, can be fabricated separately.

First check valve 82 is mounted in intake housing 58. Ball cage 126 isdisposed within intake housing 58, and first ball 128 is disposed withinball cage 126. In some examples, ball cage 126 is molded from a polymer,but it is understood that ball cage 126 can be formed from any suitablydurable material for retaining first ball 128 through repetitiveoscillation cycles. First seat 130 is disposed between ball cage 126 andinlet port 68 of intake housing 58. Second check valve 84 is disposedwithin central bore 114 of piston head 92. Retainer 136 engages aninterior surface of piston head 92, such as with threading, to securesecond seat 134 within piston head 92. In some examples, second seat 134is integrally formed on the downstream end of retainer 136. Second ball132 is disposed within piston head 92. Second seat 134 and retainer 136are fixed relative to piston head 92. First ball 128 and second ball 132can be formed from stainless steel or any other suitable material forforming a seal with first seat 130 and second seat 134, respectively.First seat 130 and second seat 134 can be formed from a high-strengthmaterial, such as tungsten carbide.

Dynamic seal 86 a is disposed between cylinder 56 and piston rod 52. Cap63 and packing nut 65 are attached to downstream end 108 of cylinder 56and retain dynamic seal 86 a within cylinder 56. Packing rings 138 a areretained on cylinder 56 such that dynamic seal 86 a remains stationarywith respect to cylinder 56 as piston 50 reciprocates relative tocylinder 56 during operation. Wear sleeve 54 is located along theportion of piston rod 52 that overlaps, along longitudinal axis L-L,with packing rings 138 a throughout the full extent of the reciprocatingmovement of piston 50. Packing rings 138 a surround and tightlyinterface with wear sleeve 54 to create a seal about piston 50, therebypreventing the pumped fluid from leaking out of downstream end 108 ofcylinder 56. Packing rings 138 a are held between seal glands 140 a.Seal glands 140 a can be metallic retaining rings, among other options.Packing rings 138 a can be formed from leather, polymer, and/or anyother suitable sealing material.

Dynamic seal 86 b is located on and around relief 119 on piston head 92and provides a fluid seal between piston head 92 and cylinder 56.Packing rings 138 b are mounted on piston head 92 and are retained byseal glands 140 b. Flange 116 extends radially from piston head 92 andis disposed at a downstream end of dynamic seal 86. Flange 116 preventsthe downstream seal gland 140 b, and thus packing rings 138 b, frommoving in the downstream direction relative to piston rod 52. Retainer136 supports the upstream seal gland 140 b to prevent seal gland 140 b,and thus packing rings 138 b, from moving in an upstream directionrelative to piston rod 52. Dynamic seal 86 b divides cylinder 56 intofirst fluid chamber 120 and second fluid chamber 122. In the exampleshown, dynamic seal 86 b reciprocates with piston rod 52 relative tocylinder 56. It is understood, however, that dynamic seal 86 b can bemounted on cylinder 56 such that dynamic seal 86 b remains stationarywith respect to cylinder 56 as piston rod 52 reciprocates relative todynamic seal 86 b. Seal glands 140 b can be metallic retaining rings,among other options. Packing rings 138 b can be formed from leather,polymer, and/or any other suitable sealing material. While displacementpump 18 is illustrated as including two dynamic seals 86, it isunderstood that displacement pump 18 can include any number of dynamicseals 86. Moreover, while dynamic seals 86 are shown as including astack of packing rings 138, it is understood that dynamic seals 86 canbe of any desired configuration, such as single polymer rings that fitaround piston rod 52 within cylinder 56, and that includes inner and/orouter projecting ribs that engage and seal with the outer surface ofpiston rod 52 and/or inner cylinder portion 124 of cylinder 56.

Piston rod body 90 extends between piston cap 88 and piston head 92.Socket 100 extends into piston cap 88. Shank 112 extends from downstreamend 108 of piston rod body 90 and into socket 100. Shank 112 is receivedin socket 100 to removably connect piston rod body 90 and piston cap 88.In some examples, socket 100 includes internal threading and shank 112includes external threading configured to mate with the internalthreading to connect piston rod body 90 and piston cap 88. It isunderstood, however, that piston rod body 90 and piston cap 88 can beconnected in any desired manner that allows for piston cap 88 to beremoved from piston rod body 90. For example, a bore can extend throughpiston cap 88 and shank 112, and a pin can be received in the bore tosecure shank 112 within socket 100. Piston head 92 is unitary withpiston rod body 90, such that piston head 92 and piston rod body 90 areformed from a single part. It is understood, however, that both pistonhead 92 and piston cap 88 can be removably connected to piston rod body90 such that piston rod 52 is formed from three separable components.Connecting portion 104 of piston cap 88 is configured to connect to adriving mechanism, such as reciprocating drive 20, to facilitatereciprocating motion of piston 50. Cap shoulder 102 is a portion ofpiston cap 88 extending radially relative to piston rod body 90. Headshoulder 118 is a portion of piston head 92 extending radially relativepiston rod body 90. Cap shoulder 102 and head shoulder 118 definecylindrical relief 142 extending around piston rod body 90. While theterms head shoulder 118 and cap shoulder 102 are used herein, it isunderstood that the cap shoulder 102 and head shoulder 118 are notnecessarily integral with piston cap 88 and piston head 92,respectively. Cap shoulder 102 and head shoulder 118 can refer to anytwo shoulders respectively closer to piston cap 88 and piston head 92for retaining wear sleeve 54. Any reference to cap shoulder 102 can bereplaced with the terms first shoulder and/or downstream shoulder, andany reference to head shoulder 118 can be replaced with the terms secondshoulder and/or upstream shoulder.

Wear sleeve 54 is tubular and is disposed on piston rod body 90. Wearsleeve 54 is coaxially aligned with piston rod 52, and specifically withpiston rod body 90. Wear sleeve 54 is disposed in cylindrical relief 142and is secured on piston rod body 90 by head shoulder 118 and capshoulder 102. First end 96 of wear sleeve 54 abuts head shoulder 118,and second end 98 of wear sleeve 54 abuts cap shoulder 102. In theexample shown, the inner surface of wear sleeve 54 contacts the radiallyouter surface of piston rod body 90 along a full length of sleeve body94. It is understood, however, that a central portion of piston rod body90 can have a reduced diameter such that a chamber is formed between thesleeve body 94 and piston rod body 90. In such an example, downstreamend 108 and upstream end 106 of piston rod body 90 are sized to maintaincontact with sleeve body 94, while the chamber extends between upstreamend 106 and downstream end 108, thereby ensuring concentricity of wearsleeve 54 and piston rod body 90. With wear sleeve 54 mounted on pistonrod 52, piston 50 has a uniform outer diameter along longitudinal axisL-L between piston cap 88, wear sleeve 54, and piston head 92.

Wear sleeve 54 can be formed from a different material than piston rod52. For example, wear sleeve 54 can be formed from metal or ceramic,among other options. Wear sleeve 54 can also be hardened prior to use.In some examples, wear sleeve 54 is formed from yttria stabilizedzirconia, aluminum oxide, tungsten carbide, and silicon nitride, amongother options. Wear sleeve 54 can thus be formed from a material that isharder than the metal of piston rod 52 such that wear sleeve 54 isbetter able to withstand the abrasive forces experienced during pumping.With wear sleeve 54 being the only component of piston 50 in contactwith dynamic seal 86 a, piston rod 52 can be formed from a softer metaland/or can undergo less hardening than that normally required towithstand the abrasion caused during pumping.

Wear sleeve 54 is removable from piston rod 52. Piston cap 88 isdetached from piston rod body 90 by rotating piston cap 88 to unscrewshank 112 from socket 100. With piston cap 88 removed, wear sleeve 54can be pulled off of piston rod body 90. Wear sleeve 54 is installed onpiston rod 52 by sliding wear sleeve 54 onto piston rod body 90 andscrewing piston cap 88 onto piston rod body 90. As such, wear sleeve 54can be quickly and efficiently replaced to provide a new wear surfacefor piston 50.

Seal groove 110 extends into upstream end 106 of piston rod body 90proximate piston head 92. Seal groove 110 receives seal 144, which isdisposed between piston rod body 90 and wear sleeve 54. Seal 144prevents the pumped fluid from migrating into the space between pistonrod body 90 and sleeve body 94. In some examples, seal 144 is an o-ring,such as an elastomer o-ring. It is understood, however, that seal 144can be of any suitable configuration for preventing the pumped fluidfrom migrating between piston rod body 90 and sleeve body 94. Forexample, seal 144 can be a gasket disposed on head shoulder 118 andcaptured between head shoulder 118 and first end 96 of wear sleeve 54.Moreover, while seal 144 is described as disposed within seal groove110, it is understood that seal 144 can be retained in any desiredmanner. For example, seal 144 can be disposed on head shoulder 118, andfirst end 96 of wear sleeve 54 can include a chamfer to accommodate seal144 and maintain seal on head shoulder 118. In other examples, wearsleeve 54 can include a groove extending into sleeve body 94 forreceiving seal 144.

During operation, piston 50 is driven through an upstroke and adownstroke along longitudinal axis L-L by a driving mechanism, such asreciprocating drive 20, to draw fluid into and drive fluid downstreamfrom displacement pump 18. During the upstroke, piston 50 is drawn inthe downstream direction, indicated by downstream arrow in FIG. 2B,along longitudinal axis L-L. As piston 50 moves in the downstreamdirection, the volume of first fluid chamber 120 increases and thevolume of second fluid chamber 122 decreases, due to piston head 92 anddynamic seal 86 b shifting in the downstream direction. The expandingfirst fluid chamber 120 experiences a vacuum condition that causes firstball 128 to shift to an open position, where first ball 128 isdisengaged from first seat 130. A flowpath is thus opened through firstcheck valve 82, and fluid is drawn into first fluid chamber 120 throughinlet port 68 and first check valve 82. During the upstroke, second ball132 is forced onto second seat 134 and forms a seal with second seat 134to prevent fluid within second fluid chamber 122 from flowing upstreaminto first fluid chamber 120. As the volume of second fluid chamber 122decreases, the fluid within second fluid chamber 122 is drivendownstream through outlet port 66 in cylinder 56.

After completing the upstroke, piston 50 reverses course and is driventhrough the downstroke. During the downstroke piston 50 is driven in theupstream direction, indicated by the upstream arrow in FIG. 2B. Duringthe downstroke, the volume of first fluid chamber 120 decreases and thevolume of second fluid chamber 122 increases. As piston 50 changes overfrom the upstroke to the downstroke second ball 132 disengages fromsecond seat 134, providing a flowpath through piston head 92 betweenfirst fluid chamber 120 and second fluid chamber 122. First ball 128engages first seat 130, closing first check valve 82 and preventingfluid from backflowing from first fluid chamber 120 through inlet port68. As piston 50 moves through the downstroke, the fluid within firstfluid chamber 120 flows downstream to second fluid chamber 122 throughretainer 136, piston head 92, second check valve 84, and piston port 146(shown in FIGS. 3A-4B and 5B-6B). Outlet port 66 is in unobstructedfluid communication with second fluid chamber 122, and as will beappreciated, fluid is driven downstream through outlet port 66 duringboth the upstroke and the downstroke of piston 50.

During both the upstroke and the downstroke dynamic seals 86 preventfluid and air from flowing between the inner surface of cylinder 56 andthe outer surface of piston 50. Both dynamic seals 86 are tightlytoleranced to build the vacuum condition in first fluid chamber 120 andsecond fluid chamber 122, and to apply positive pressure during thereciprocation cycle of piston 50. Wear sleeve 54 is the only portion ofpiston 50 that contacts dynamic seal 86 a during reciprocation of piston50. As such, wear sleeve 54 prevents any portion of dynamic seal 86 afrom contacting any portion of piston rod 52, including piston cap 88,piston rod body 90, and piston head 92. Wear sleeve 54 thus protectspiston rod 52 from experiencing wear caused by relative movement at theinterface of piston rod 52 and dynamic seal 86 a.

Wear sleeve 54 provides significant advantages. Wear sleeve 54experiences all of the abrasive forces caused by reciprocating movementof piston 50 relative to dynamic seal 86 a. With wear sleeve 54 beingthe only portion of piston 50 experiencing wear generated by dynamicseal 86 a during reciprocation, piston rod 52 can be formed from asofter metal and/or can undergo less hardening, thereby reducingmanufacturing costs. Moreover, wear sleeve 54 can easily be removed andreplaced on piston rod 52 by unscrewing piston cap 88 from piston rodbody 90, pulling wear sleeve 54 off of piston rod body 90, and replacinga new wear sleeve 54 on piston rod body 90. Wear sleeve 54 beingremovable saves costs and decreases downtime that would previously berequired to replace a worn piston 50. In particularly abrasiveenvironments, wear sleeve 54 can be made of a suitably sturdy, yetcheap, material to facilitate multiple replacements throughout thepumping process while utilizing a single piston 50.

FIG. 3A is an exploded view of piston 50. FIG. 3B is a cross-sectionalview of piston 50. FIGS. 3A and 3B will be discussed together. Piston 50includes piston rod 52 and wear sleeve 54. Piston rod 52 includes pistoncap 88, piston rod body 90, and piston head 92. Wear sleeve 54 includessleeve body 94, first end 96 and second end 98. Piston cap 88 includessocket 100, cap shoulder 102, and connecting portion 104. Piston rodbody 90 includes upstream end 106, downstream end 108, seal groove 110,and shank 112. Piston head 92 includes central bore 114, flange 116,head shoulder 118, and piston port 146.

Piston rod body 90 is unitary with and extends longitudinally frompiston head 92. Central bore 114 extends into piston head 92 and isconfigured to receive a check valve, such as second check valve 84(shown in FIGS. 2B and 4). Piston port 146 extends through piston head92 and provides a flowpath for fluid to flow downstream out of pistonhead 92. Flange 116 extends radially from piston head 92 and isconfigured to support a seal, such as dynamic seal 86 b (shown in FIGS.2B and 4) mounted around relief 119. Head shoulder 118 extends radiallyfrom piston head 92 relative to piston rod body 90 and is disposedproximate upstream end 106 of piston rod body 90. Seal groove 110extends into upstream end 106 of piston rod body 90. Seal groove 110receives seal 144.

Shank 112 extends from downstream end 108 of piston rod body 90 and isconfigured to engage socket 100. Shank 112 is secured within socket 100to attach piston rod body 90 to piston cap 88. Connecting portion 104extends from piston cap 88 and is configured to interface with a drivingmechanism, such as reciprocating drive 20 (shown in FIG. 1B), tofacilitate reciprocating movement of piston 50. Cap shoulder 102 extendsradially from piston cap 88 relative to piston rod body 90. In someexamples, shank 112 includes external threading configured to mate withinternal threading in socket 100. In other examples, a bore extendsthrough shank 112 and socket 100 and the bore is configured to receive apin to secure shank 112 within socket 100, thereby connecting piston cap88 and piston rod body 90.

Cap shoulder 102 and head shoulder 118 define cylindrical relief 142,which extends axially along the length of piston rod body 90 betweenpiston cap 88 and piston head 92. Wear sleeve 54 is disposed on pistonrod body 90 in cylindrical relief 142 and extends between piston cap 88and piston head 92. Sleeve body 94 is cylindrical and receives pistonrod body 90. With wear sleeve 54 disposed on piston rod body 90, firstend 96 of wear sleeve 54 abuts head shoulder 118 and second end 98 ofwear sleeve 54 abuts cap shoulder 102.

Wear sleeve 54 is secured on piston rod body 90 by head shoulder 118 andcap shoulder 102. Wear sleeve 54 covers piston rod body 90 such thatpiston rod body 90 is prevented from contacting abrasive wear surfaces,such as dynamic seal 86 a (shown in FIGS. 2B and 4) during operation.Wear sleeve 54 is a replaceable wear component of piston 50 thatincreases the lifespan of piston rod 52 by preventing direct contactbetween piston rod 52 and dynamic seal 86 a. With wear sleeve 54 mountedon piston rod 52, piston 50 has a uniform outer diameter between pistoncap 88, wear sleeve 54, and piston head 92. As discussed above, wearsleeve 54 can be made from any desired material, such as metal orceramic.

Wear sleeve 54 is mechanically secured on piston rod 52. No adhesive isutilized to secure wear sleeve 54 on piston rod 52. Mechanicallysecuring wear sleeve 54 on piston rod 52 facilitates removal andreplacement of wear sleeve 54. The clamping force exerted on wear sleeve54 by head shoulder 118 and cap shoulder 102 secures wear sleeve 54 onpiston rod 52. To remove wear sleeve 54, piston cap 88 is rotatedrelative to piston rod body 90 to unthread shank 112 from socket 100,and piston cap 88 is pulled off of piston rod body 90. With piston cap88 removed, wear sleeve 54 can be pulled off of piston rod body 90. Toinstall wear sleeve 54 on piston rod 52, wear sleeve 54 is slid ontopiston rod body 90 such that shank 112 extends out of second end 98 ofwear sleeve 54. Piston cap 88 is attached to piston rod body 90 bythreading shank 112 into socket 100. With piston cap 88 reattached topiston rod body 90 wear sleeve 54 is secured between head shoulder 118and cap shoulder 102.

Wear sleeve 54 provides significant advantages. Wear sleeve 54 protectspiston rod 52 from experiencing wear due to moving relative to dynamicseal 86 a. With wear sleeve 54 experiencing all wear caused by dynamicseal 86 a, piston rod 52 can be manufactured from a softer metal and/orcan undergo less hardening, thereby saving manufacturing costs. Inaddition, wear sleeve 54 is replaceable, thereby extending the usefullife of piston rod 52 by allowing the user to replace wear sleeve 54 andcontinue using the same piston rod 52, which saves replacement costs.Wear sleeve 54 is retained on piston rod body 90 by head shoulder 118and cap shoulder 102 without the use of adhesives, which facilitatesquick and efficient removal and replacement of wear sleeve 54.

FIG. 4A is an exploded view of piston 50′. FIG. 4B is a cross-sectionalview of piston 50′. Piston 50′ includes piston rod 52′ and wear sleeve54. Piston rod 52′ includes piston cap 88′, piston rod body 90′, andpiston head 92′. Wear sleeve 54 includes sleeve body 94, first end 96and second end 98. Piston cap 88′ includes cap shoulder 102′ andconnecting portion 104′. Piston rod body 90′ includes upstream end 106′,downstream end 108′, seal groove 110′, and shank 112′. Piston head 92′includes socket 100′, central bore 114′, flange 116′, head shoulder118′, relief 119′, and piston port 146′.

Piston rod body 90′ is unitary with and extends longitudinally frompiston cap 88′. Connecting portion 104′ extends from piston cap 88′ andis configured to engage a driving member, such as reciprocating drive 20(shown in FIG. 1B), to facilitate reciprocating movement of piston 50′.Cap shoulder 102′ extends radially from piston cap 88′ relative topiston rod body 90′ and is disposed proximate downstream end 108′ ofpiston rod body 90′. Shank 112′ extends from upstream end 106′ of pistonrod body 90′ and includes external threading. Seal groove 110′ extendsinto upstream end 106′ of piston rod body 90′ proximate shank 112′, andseal groove 110′ receives seal 144. Seal 144 can be any suitable sealfor preventing fluid from migrating into the interface between wearsleeve 54 and piston rod body 90′. For example, seal 144 can be anelastomer o-ring.

Socket 100′ extends into a downstream end of piston head 92′ and centralbore 114′ extends into an upstream end of piston head 92′. Socket 100′includes internal threading configured to mate with external threadingon shank 112′ to attach piston head 92′ and piston rod body 90′. Pistonport 146′ extends through piston head 92′ and is in fluid communicationwith central bore 114′. Piston port 146′ provides a flowpath for fluidto flow downstream out of piston head 92′. Flange 116′ extends radiallyfrom piston head and is configured to support a seal, such as dynamicseal 86 b (shown in FIGS. 2B and 5A) mounted around relief 119′. Headshoulder 118′ is formed on a portion of piston head 92′ extendingradially relative to piston rod body 90′.

Cap shoulder 102′ and head shoulder 118′ define cylindrical relief 142′,which extends along the length of piston rod body 90′ between piston cap88′ and piston head 92′. Wear sleeve 54 is disposed in cylindricalrelief 142′ and extends between piston cap 88′ and piston head 92′.Sleeve body 94 is cylindrical and surrounds piston rod body 90′. Firstend 96 of wear sleeve 54 abuts head shoulder 118′ and second end 98 ofwear sleeve 54 abuts cap shoulder 102′. With wear sleeve 54 mounted onpiston rod 52′, piston 50′ has a uniform outer diameter between pistoncap 88′, wear sleeve 54, and piston head 92′. Wear sleeve 54 coverspiston rod body 90′ such that piston rod body 90′ is prevented fromcontacting abrasive wear surfaces, such as dynamic seal 86 a, as piston50′ reciprocates during operation. Wear sleeve 54 is a replaceable wearcomponent of piston 50′ that increases the lifespan of piston rod 52′.As discussed above, wear sleeve 54 can be made from any desiredmaterial, such as metal or ceramic.

Wear sleeve 54 is mechanically secured on piston rod 52′ by a clampingforce exerted on wear sleeve 54 by head shoulder 118′ and cap shoulder102′. No adhesive is utilized to secure wear sleeve 54 on piston rod52′. Mechanically securing wear sleeve 54 facilitates removal andreplacement of wear sleeve 54. To remove wear sleeve 54, piston head 92′is rotated relative to piston rod body 90′ to unthread shank 112′ fromsocket 100′. Piston head 92′ is pulled off of piston rod body 90′. Withpiston head 92′ removed, wear sleeve 54 is pulled off of piston rod body90′. To install wear sleeve 54 on piston rod 52′, wear sleeve 54 is slidonto piston rod body 90′ such that shank 112′ extends out of first end96 of wear sleeve 54. Piston head 92′ is attached to piston rod body 90′by threading shank 112′ into socket 100′. With piston head 92′reattached to piston rod body 90′, wear sleeve 54 is secured betweenhead shoulder 118′ and cap shoulder 102′.

FIG. 5A is a cross-sectional view of displacement pump 18 includingpiston 50″. FIG. 5B is an exploded view of piston 50″. FIG. 5C is across-sectional view of piston 50″. FIGS. 5A-5C will be discussedtogether. Displacement pump 18 is functionally similar to displacementpump 18 shown in FIGS. 2A-2B. As such, like numbers are used to describelike parts and the operation and arrangement of the like parts will notbe discussed in detail.

Piston 50″ includes piston rod 52″ and wear sleeve 54. Piston rod 52″includes piston cap 88″, piston rod body 90″, and piston head 92″. Wearsleeve 54 includes sleeve body 94, first end 96, and second end 98.Piston cap 88″ includes cap shoulder 102″, connecting portion 104″, andshank 112″. Piston rod body 90″ includes socket 100″, upstream end 106″,downstream end 108″, and seal groove 110″. Piston head 92″ includescentral bore 114″, flange 116″, head shoulder 118″, relief 119″, andpiston port 146″.

Piston 50″ extends along longitudinal axis L-L and is configured todrive fluid through displacement pump 18. Piston rod 52″ extends intocylinder through cap 63 and packing nut 65 and is elongate alonglongitudinal axis L-L. Piston rod 52″ can be formed from any suitablydurable material for withstanding the high pressures associated withpumping. For example, piston 50″ can be machined or cast from steel,brass, aluminum, or any other suitable metal. In some examples, piston50″ can be formed from hardened 440C stainless steel.

Shank 112″ extends from piston cap 88″ and is received within socket100″. In some examples, socket 100″ includes internal threading andshank 112″ includes external threading configured to mate with theinternal threading in socket 100″ to secure piston cap 88″ to piston rodbody 90″. In other examples, a bore can extend through socket 100″ andshank 112″, and the bore can receive a pin to secure piston cap 88″ topiston rod body 90″. As such, piston cap 88″ is removably connected topiston rod body 90″. Connecting portion 104″ of piston cap 88″ isconfigured to connect piston 50″ to a driving mechanism that drives thereciprocating motion of piston 50″ during operation. As shown,connecting portion 104″ includes an aperture for receiving a pin that isdriven in a reciprocating manner by a drive, such as reciprocating drive20 (shown in FIG. 2B), to facilitate reciprocation of piston 50″. Capshoulder 102″ extends radially from piston cap 88″ relative to pistonrod body 90″.

Piston rod body 90″ is unitary with piston head 92″ and is elongatealong longitudinal axis L-L. Socket 100″ extends into downstream end108″ of piston rod body 90″ and receives shank 112″. Socket 100″ caninclude internal threading configured to mate with external threading onshank 112″, such that the interfacing threads secure piston cap 88″ topiston rod body 90″. Seal groove 110″ extends into upstream end 106″ ofpiston rod body 90″ proximate piston head 92″. Seal 144 is at leastpartially disposed within seal groove 110″. Seal 144 provides afluid-tight seal between piston rod body 90″ and wear sleeve 54 and canbe of any desired configuration for preventing the pumped fluid fromflowing into the interface between piston rod body 90″ and sleeve body94. In some examples, seal 144 is an o-ring, such as an elastomero-ring. It is understood, however, that seal 144 can be of any suitableconfiguration for preventing the pumped fluid from migrating betweenpiston rod body 90″ and wear sleeve 54.

Head shoulder 118″ extends radially from piston head 92″ relative topiston rod body 90″. Central bore 114″ extends into an upstream end ofpiston head 92″ and receives second check valve 84. Piston port 146″extends through piston head 92″ downstream of second check valve 84, andpiston port 146″ provides a flowpath between central bore 114″ andsecond fluid chamber 122, to allow the pumped fluid to flow downstreamout of piston head 92″. Flange 116″ extends radially from piston head92″ and provides downstream support for dynamic seal 86 b to preventdynamic seal 86 b from shifting downstream during reciprocation ofpiston 50″. Dynamic seal 86 b is disposed around relief 119″ on pistonhead 92″.

Head shoulder 118″ and cap shoulder 102″ define cylindrical relief 142″,which extends along the longitudinal length of piston rod body 90″. Wearsleeve 54 is disposed in cylindrical relief 142″ and surrounds pistonrod body 90″. Sleeve body 94 is tubular and is configured to receivepiston rod body 90″. Wear sleeve 54 is located along the portion ofpiston rod 52″ that overlaps, along longitudinal axis L-L, with packingrings 138 a throughout the full extent of the reciprocating movement ofpiston rod 52″. Wear sleeve 54 is coaxially aligned with piston rod 52″,and specifically with piston rod body 90″. First end 96 of wear sleeve54 abuts head shoulder 118″ and second end 98 of wear sleeve 54 abutscap shoulder 102″. While the terms head shoulder 118″ and cap shoulder102″ are used herein, it is understood that the cap shoulder 102″ andhead shoulder 118″ are not necessarily integral with piston cap 88″ andpiston head 92″, respectively. Cap shoulder 102″ and head shoulder 118″can refer to any two shoulders respectively closer to piston cap 88″ andpiston head 92″ for retaining wear sleeve 54. Any reference to capshoulder 102″ can be replaced with the terms first shoulder and/ordownstream shoulder, and any reference to head shoulder 118″ can bereplaced with the terms second shoulder and/or upstream shoulder.

Wear sleeve 54 is mechanically secured on piston rod body 90″ by headshoulder 118″ and cap shoulder 102″. No adhesive is utilized to securewear sleeve 54 on piston rod 52″. Mechanically securing wear sleeve 54on piston rod body 90″ facilitates removal and replacement of wearsleeve 54. To remove wear sleeve 54 from piston rod 52″, piston cap 88″is rotated relative to piston rod body 90″ to unthread shank 112″ fromsocket 100″. Piston cap 88″ is pulled away from piston rod body 90″.With piston cap 88″ removed, wear sleeve 54 is pulled off of piston rodbody 90″. To install wear sleeve 54 on piston rod 52″, wear sleeve 54 isslid onto piston rod body 90″. Piston cap 88″ is attached to piston rodbody 90″ by threading shank 112″ into socket 100″. With piston head 92″reattached to piston rod body 90″, wear sleeve 54 fully encloses pistonrod body 90″ and is secured between head shoulder 118″ and cap shoulder102″.

During operation, piston 50″ reciprocates within cylinder 56 andrelative to dynamic seal 86 a. Wear sleeve 54 is the only portion ofpiston 50″ that contacts dynamic seal 86 a during reciprocation ofpiston 50″. As such, wear sleeve 54 prevents any portion of dynamic seal86 a from contacting piston rod 52″, which include piston cap 88″,piston rod body 90″, and piston head 92″. Wear sleeve 54 experiences allof the abrasive forces generated at the interface of dynamic seal 86 aand piston 50″. Wear sleeve 54 thus protects piston rod 52″ fromexperiencing wear caused by movement relative to dynamic seal 86 a.

As discussed above, wear sleeve 54 can be formed from a differentmaterial than piston rod 52″. Piston rod 52″ is typically metallic. Wearsleeve 54 can be formed from metal or ceramic, among other options, andwear sleeve 54 can be hardened prior to use. In some examples, wearsleeve 54 is formed from yttria stabilized zirconia, aluminum oxide,tungsten carbide, and silicon nitride, among other options. Wear sleeve54 can thus be formed from a material that is harder than the metal ofpiston rod 52″, such that wear sleeve 54 is better able to withstand theabrasive forces experienced during pumping. In examples where wearsleeve 54 is formed from metal, the metal of wear sleeve 54 can bedifferent than the metal of piston rod 52″ and/or can be treated, suchas heat treating, to have different properties than piston rod 52″. Withwear sleeve 54 being the only component of piston 50″ in contact withdynamic seal 86 a, piston rod 52″ can be formed from a softer metaland/or can undergo less hardening than that normally required towithstand the abrasion experienced during pumping. In some examples,wear sleeve 54 is made from the same material as piston rod 52″. It isunderstood, however, that regardless of the material that wear sleeve 54is made from, wear sleeve 54 is the only portion of piston 50″ thatinterfaces with dynamic seal 86 a during operation.

Wear sleeve 54 provides significant advantages. Wear sleeve 54experiences all of the abrasive forces caused by reciprocating movementof piston 50″ relative to dynamic seal 86 a. With wear sleeve 54 beingthe only portion of piston 50″ experiencing wear generated duringreciprocation, piston rod 52″ can be formed from a softer metal and/orcan undergo less hardening, thereby reducing manufacturing costs.Moreover, wear sleeve 54 can easily be removed and replaced on pistonrod 52″, by unscrewing piston cap 88″ from piston rod body 90″, pullingwear sleeve 54 off of piston rod body 90″, and replacing a new wearsleeve 54 on piston rod body 90″. Wear sleeve 54 being removable savescosts and decreases downtime that would previously be required toreplace a worn element of piston 50″. Wear sleeve 54 eliminates the needto replace piston rod 52″, thereby decreasing operating costs.

FIG. 6A is an exploded view of piston 50′″. Piston 50′″ includes pistonrod 52′″ and wear sleeve 54. Piston rod 52′″ includes piston cap 88′″,piston rod body 90′″, and piston head 92′″. Wear sleeve 54 includessleeve body 94, first end 96, and second end 98. Piston cap 88′″includes cap shoulder 102′″ and connecting portion 104′″. Piston rodbody 90′″ includes socket 100′″, upstream end 106′″, and downstream end108′″. Piston head 92′″ includes shank 112′″, central bore 114′″, flange116′″, head shoulder 118′″, and piston port 146′″. Shank 112′″ includesseal groove 110′″.

Piston rod body 90′″ is unitary with and extends longitudinally frompiston cap 88′″. Connecting portion 104′″ is disposed on piston cap 88′″and is configured to engage a driving member, such as reciprocatingdrive 20, to facilitate reciprocation of piston 50′″ during operation.In the example shown, connecting portion 104′″ includes an apertureextending therethrough that is configured to receive a pin to drivepiston 50′″ in a reciprocating manner. Cap shoulder 102′″ extendsradially from piston cap 88′″ relative to piston rod body 90′″. Capshoulder 102′″ is disposed proximate downstream end 108′″ of piston rodbody 90′″. Socket 100′″ extends into upstream end 106′″ of piston rodbody 90′″. In some examples socket 100′″ includes internal threading.

Shank 112′″ extends from a downstream end of piston head 92′″. In someexamples, shank 112′″ includes external threading configured to matewith the internal threading of socket 100′″. As such, shank 112′″ can bethreaded into socket 100′″ to secure piston head 92′″ to piston rod body90′″. Seal groove 110′″ extends circumferentially around shank 112′″.Seal 144 is at least partially disposed in seal groove 110′″. Centralbore 114′″ extends into an upstream end of piston head 92′″. Piston port146′″ extends through piston head 92′″ and is in fluid communicationwith central bore 114′″. Piston port 146′″ provides a flowpath for fluidto flow downstream out of piston head 92′″. Flange 116′″ extendsradially from piston head and is configured to support a seal, such asdynamic seal 86 b (shown in FIGS. 2B and 5A). Head shoulder 118′″extends radially from piston head 92′″ relative to piston rod body 90′″.

Cap shoulder 102′″ and head shoulder 118′″ define cylindrical relief142′″, which extends along the length of piston rod body 90′″ betweenpiston cap 88′″ and piston head 92′″. Wear sleeve 54 is disposed incylindrical relief 142′″. Sleeve body 94 is cylindrical and surroundpiston rod body 90′″. First end 96 of wear sleeve 54 abuts head shoulder118′″ and second end 98 of wear sleeve 54 abuts cap shoulder 102′″. Withwear sleeve 54 mounted on piston rod 52′″, piston rod 52′″ has a uniformouter diameter between piston cap 88′″, wear sleeve 54, and piston head92′″. Wear sleeve 54 encloses piston rod body 90′″ such that piston rodbody 90′″ is prevented from contacting abrasive wear surfaces, such asdynamic seal 86 a, during operation. Wear sleeve 54 is a replaceablewear component of piston 50′″. As discussed above, wear sleeve 54 can bemade from any desired material, such as metal or ceramic.

Wear sleeve 54 is mechanically secured on piston rod 52′″ by a clampingforce exerted on wear sleeve 54 by head shoulder 118′″ and cap shoulder102′″. No adhesive is utilized to secure wear sleeve 54 on piston rod52′″. Mechanically securing wear sleeve 54 facilitates removal andreplacement of wear sleeve 54. To remove wear sleeve 54 from piston rod52′″, piston head 92′″ is rotated relative to piston rod body 90′″,unthreading shank 112′″ from socket 100′″. Piston head 92′″ is pulledoff of piston rod body 90′″. With piston head 92′″ removed, wear sleeve54 is pulled off of piston rod body 90′″. To install wear sleeve 54 onpiston rod 52′″, wear sleeve 54 is slid onto piston rod body 90′″.Piston head 92′″ is attached to piston rod body 90′″ by threading shank112′″ into socket 100′″. With piston head 92′″ reattached to piston rodbody 90′″, wear sleeve 54 is secured between head shoulder 118′″ and capshoulder 102′″.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

What is claimed is:
 1. A piston for a displacement pump, the pistoncomprising: a piston rod body elongate along an axis between a first endand a second end; a piston head connected to the second end; acylindrical relief extending around the piston rod body; and a wearsleeve disposed about the piston rod body within the cylindrical relief;wherein the piston rod body is removably connected to the piston head bya mounting portion of the piston rod extending into a receiving portionof the piston head; and wherein the mounting portion is received insidethe receiving portion.
 2. The piston of claim 1, wherein the receivingportion is a socket formed in the piston head and the mounting portionis a shank projecting from the second end.
 3. The piston of claim 2,wherein the shank extends axially from the second end.
 4. The piston ofclaim 2, wherein interfaced threading is formed on the socket and theshank, the interfaced threading securing the piston head to the pistonrod body.
 5. The piston of claim 1, wherein a check valve is disposed inthe piston head.
 6. The piston of claim 1, wherein a dynamic seal isdisposed on an exterior surface of the piston head.
 7. The piston ofclaim 6, wherein the dynamic seal is formed from a plurality of packingrings.
 8. The piston of claim 1, further comprising: a piston capdisposed at the first end, the piston cap including aradially-projecting connecting portion.
 9. The piston of claim 1,wherein the piston head includes a first head end and a second head end,the receiving portion extending into the first head end and a centralbore extending into the second head end, wherein at least one portextends through an exterior surface of the piston head and is in fluidcommunication with the central bore.
 10. The piston of claim 9, whereinthe piston head includes a flange extending radially from an exteriorsurface of the piston head.
 11. The piston of claim 10, wherein a reliefis formed on the piston head between the second head end and the flange,the relief configured to receive a dynamic seal.
 12. The piston of claim10, wherein at least a portion of the at least one port extends throughthe flange.
 13. The piston of claim 9, wherein the piston head includesa head shoulder formed at the first head end, the head shoulder at leastpartially defining the cylindrical relief.
 14. A displacement pump for aspraying system, the displacement pump comprising: a cylinder having anupstream end and a downstream end; a first dynamic seal mounted in thecylinder; and the piston of claim 1, wherein the piston extends into thecylinder through the first dynamic seal; wherein the piston isconfigured to reciprocate within the cylinder and relative to the firstdynamic seal; and wherein the wear sleeve is disposed between the firstdynamic seal and the piston such that the wear sleeve is the only partof the piston contacting the first dynamic seal during reciprocation.15. The displacement pump of claim 14, further comprising: a seconddynamic seal disposed on an exterior surface of the piston head, whereinthe second dynamic seal is configured to reciprocate relative to thecylinder.
 16. A piston for a displacement pump, the piston comprising: apiston rod body elongate along an axis between a first end and a secondend; a piston head connected to the second end; and a first dynamic sealmounted on an exterior surface of the piston head; wherein the pistonrod body is removably connected to the piston head by a mounting portionof the piston rod extending into a receiving portion of the piston head;wherein the receiving portion is a socket formed in the piston head andthe mounting portion is a shank projecting from the second end; andwherein the shank includes external threads and the socket includesinternal threads configured to mate with the external threads to securethe piston head to the piston rod body.
 17. A piston for a displacementpump, the piston comprising: a piston rod body elongate along an axisbetween a first end and a second end; a piston head connected to thesecond end; and a first dynamic seal mounted on an exterior surface ofthe piston head; wherein the piston rod body is removably connected tothe piston head by a mounting portion of the piston rod extending into areceiving portion of the piston head; wherein the piston head includes afirst head end and a second head end, the receiving portion extendinginto the first head end and a central bore extending into the secondhead end, and wherein at least one port extends through an exteriorsurface of the piston head and is in fluid communication with thecentral bore.
 18. The piston of claim 17, wherein the piston headincludes a flange extending radially from an exterior surface of thepiston head, and wherein the at least one port is disposed on a firstside of the flange and the first dynamic seal is disposed on a secondside of the flange.